Waveform generation method, radar device, and oscillator for radar device

ABSTRACT

It is possible to generate D/A conversion voltage in which an error generated by numeric irregularities of a D/A conversion element such as resistor constituting a D/A converter 11 is corrected. A waveform generation method characterized in that input data into a D/A converter  11  are provided to the D/A converter in order at a timing at which a voltage of a desired waveform which has D/A conversion data indicating a conversion amount of the input data obtained by varying the input data by a minimum conversion unit or a unit obtained by multiplying the minimum conversion unit by an integer, and which varies with time series, becomes substantially equal to a D/A-converted voltage, whereby the D/A-converted voltage is generated in accordance with the desired waveform.

CROSS-REFERENCE

This application is a continuation of U.S. Ser. No. 10/572,964, filed onMar. 21, 2006, the entire contents of each which are incorporated hereinby reference, which claims the benefit of priority under 35 U.S.C. § 120from PCT/JP05/02911, filed Feb. 23, 2005, all of which claim the benefitof priority under 35 U.S.C. § 119 from Japanese Patent Application No.JP 2004-049586, filed Feb. 25, 2004.

TECHNICAL FIELD

This invention relates to a waveform generation method adapted togenerate a waveform programmably, and a radar device provided withwaveform generation means adapted to generate a waveform programmably.

BACKGROUND ART

In a conventional waveform generation method, output levels of a D/Aconverter are set at regular intervals, and a conversion timing isvaried at a predetermined ratio, a desired signal is thereby obtained(for example, refer to the Patent Document 1).

In a conventional radar device, data obtained by correcting a linearityof an oscillating frequency of VCO occurring due to a non-linearity andthe like of D/A converter, LPF, and VCO, which are provided between CPUand a voltage control oscillator (which will hereinafter be referred toas VCO), are provided to D/A converter at regular timing intervals (forexample, refer to Patent Document 2).

Patent Document 1: JP-A-61-144930 (page 3, left lower column, FIG. 3)

Patent Document 2: JP-A-2002-156447 (page 4, left column to page 5,right column, FIG. 1, FIG. 6)

DISCLOSURE OF THE INVENTION Problems that the Invention is to Solve

When data are provided to a plurality of input terminals of D/Aconverter in a conventional waveform generation method, a voltage valuesubjected to D/A conversion by each input terminal is supposed to beconstant. Therefore, an error of a voltage value occurring in each inputterminal due to numeric irregularities of a D/A conversion element, suchas a resistor etc. constituting the D/A converter and to be D/Aconverted is not taken into consideration. This caused the accuracy of awaveform to be deteriorated.

When conversion data including data on a D/A converter are measured inconventional radar device, the data inputted into the D/A converter aredifferent from a minimum conversion unit, and values among the measureddata are generated by interpolation based on approximation. Therefore,errors of D/A conversion voltage values generated in each input terminaldue to numeric irregularities of the D/A conversion element, such as aresistor, etc. are not taken into consideration, and, therefore, theaccuracy of a generated waveform was deteriorated. Since the accuracy ofthe generated waveform is deteriorated, the accuracy of the oscillationfrequency of VCO oscillated on the basis of the generated waveform isalso deteriorated. Therefore, in radar device for measuring a distancebetween the radar device and an object on the basis of a frequencyreflected on the object, or a relative velocity with respect to theobject, the measuring accuracy of the radar device was deteriorated. Inorder to improve the measuring accuracy, it is necessary to employ anexpensive D/A having an increased bit number to cause a price of theradar device to become high.

The present invention has been made so as to solve these problems, andprovides a waveform generation method and radar device which are capableof improving the accuracy of a waveform to be generated, even when a D/Aconversion element, such as a resistor, etc. had numeric irregularities.

Means for Solving the Problems

In the waveform generation method according to the present invention, avoltage D/A converted in accordance with a desired waveform is generatedon the basis of the D/A conversion data obtained by varying input datainto the D/A converter by a minimum conversion unit, or by a unitobtained by multiplying the minimum conversion unit by an integer.

In the radar device according to the present invention, a voltage D/Aconverted in accordance with a desired waveform is generated on thebasis of the D/A conversion data obtained by varying input data into theD/A converter by a minimum conversion unit, or by a unit obtained bymultiplying the minimum conversion unit by an integer, and the voltageis provided to the oscillating means to thereby vary the oscillationfrequency.

Advantage of the Invention

The present invention becomes able to generate a voltage in which anerror occurring due to a scatter of the numerical value of a D/Aconversion element, such as a resistor constituting the D/A converterwere corrected, by generating a D/A conversion voltage in accordancewith a desired voltage on the basis of D/A conversion data obtained byvarying input data into the D/A converter by a minimum conversion unit,or by a unit obtained by varying the minimum conversion unit bymultiplying the minimum conversion unit by an integer.

BRIEF DESCRIPTION OF THE DRAWINGS

[FIG. 1] It is a block diagram of a waveform generation method showingan embodiment 1 of the present invention.

[FIG. 2] It is a waveform diagram describing an example of thegeneration of D/A conversion data showing the embodiment 1 of thepresent invention.

[FIG. 3] It is a waveform diagram showing an example of the generationof desired D/A input data shown in the embodiment 1 of the presentinvention.

[FIG. 4] It is a drawing of storage data in which desired D/A input datashowing the embodiment 1 of the present invention are stored in aninternal memory of a microcomputer 1.

[FIG. 5] It is a block diagram of a waveform generation method showingan embodiment 2 of the present invention.

[FIG. 6] It is a block diagram of waveform generation method showing anembodiment 3 of the present invention.

[FIG. 7] It is a block diagram of a FMCW radar device showing anembodiment 4 of the present invention.

[FIG. 8] It is a frequency variation diagram used to calculate arelative distance between the radar device and an object and a relativevelocity thereof showing the embodiment 4 of the present invention.

[FIG. 9] It is a waveform of a desired waveform signal showing theembodiment 4 of the present invention.

BRIEF DESCRIPTION OF THE DRAWINGS

1 Microcomputer

2 D/A converter

3 LPF

4 Voltmeter

5 D/A conversion voltage signal

6 Desired waveform signal

7 Microcomputer

8 Voltmeter

9 IC tester

10 Microcomputer

11 VCO

12 Directional coupler

13 Transmission antenna

14 Mixer

15 Reception antenna

16 Amplifier

17 A/D converter

18 Transmission frequency

19 Reception frequency

20 Desired waveform signal

BEST MODE FOR CARRYING OUT THE INVENTION Embodiment 1

FIG. 1 shows a block diagram of the waveform generation method in anembodiment 1 for carrying out this invention. In FIG. 1, the data (whichwill hereinafter be referred to as desired D/A input data) in accordancewith a desired voltage waveform (which will hereinafter be referred toas desired waveform) stored in advance in a memory (not shown) containedin a microcomputer 1 are provided to a D/A converter 2, to generate avoltage (which will hereinafter be referred to as D/A conversionvoltage) D/A converted in accordance with the desired waveform. This D/Aconversion voltage is then passed through a low-pass filter LPF 3 toobtain a LPF output signal from which a high-frequency componentoccurring with the D/A conversion is eliminated.

When the desired D/A input data are generated, the microcomputer 1 givesdata (which will hereinafter be referred to as measured D/A input data)obtained by increasing in order by a minimum conversion unit of the D/Aconverter 2, or by a unit obtained by multiplying the minimum conversionunit by an integer, to the D/A converter 2, and an actual D/A conversionvoltage is measured with a voltmeter 4 as a voltage measuring means toobtain data (which will hereinafter be referred to as D/A conversiondata) corresponding to the D/A conversion voltage with respect to eachmeasured D/A input data. A desired D/A input data are then generated byextracting the measured D/A input data at a timing at which a voltage ofa desired waveform varying with time series and the D/A conversionvoltage in the D/A conversion data become equal to each other.

The method of generating desired D/A input data in this embodiment willnow be described with reference to FIG., 2 to FIG. 4. In the followingdescription, measured D/A input data mentioned above are used as aminimum conversion unit of the D/A converter 2. This can also be appliedto a case where the measured D/A input data are used as a unit obtainedby multiplying the minimum conversion unit by an integer.

First, the method of generating the D/A conversion data will bedescribed with reference to FIG. 2. FIG. 2 is a waveform diagram showingan example of the generation of D/A conversion data generated in advanceof the generation of the desired D/A input data. In FIG. 2, the lateralaxis represents measured D/A input data provided to the D/A converter 2,and the longitudinal axis D/A conversion voltage measured with thevoltmeter 4. The data are shown with the input bit number of 8 of theD/A converter 2. The measured D/A input data is 00(h) to FF(h) inhexadecimal notation, the D/A conversion voltage is 256 stages of V0 toV255.

The measured D/A input data are provided by the microcomputer 1 to theD/A converter 2 so that the data increase in order by one count from00(h) to FF(h) to generate D/A conversion voltage signal 5. On eachstage, a voltage of the D/A conversion voltage signal 5 is measured withthe voltmeter 4 to obtain D/A conversion voltage V0 to V255.

The D/A converter 2 mentioned above generates an error of voltage to beD/A converted by each bit of an input terminal due to numericirregularities of a D/A conversion element, such as a resistor etc.constituting the D/A converter 2. Therefore, the variation range of theD/A conversion voltage varying by each count of the D/A input data ismeasured as shown in FIG. 2 as the range varied in each count, or as therange varied periodically in accordance with the weight of each bit.

A method of forming desired D/A input data will be described withreference to FIG. 3 and FIG. 4. FIG. 3 is a waveform diagram showing anexample of generation of desired D/A input data, and FIG. 4 is a drawingof storage data registered in the internal memory of the microcomputer1. In FIG. 3, a lateral axis represents time, and a longitudinal axisrepresents a voltage. The longitudinal axis shows D/A conversion voltageV0 to V255 measured by the D/A conversion data generating methodmentioned above. A timing t1 to t256 at which a desired waveform signal6 shown with time series stored in advance in the internal memory in themicrocomputer 1 crosses the D/A converted voltages V0 to V255 are shownon the lateral axis.

Each measured D/A input data at each timing of t1 to t256 can beobtained as desired D/A input data as shown in FIG. 4, by the abovetiming t1 to t256 and each measured D/A input data of 00(h) to FF(h)which generate each D/A conversion voltage of V0 to V255.

When the determination of the timing at which the desired waveformsignal 6 crosses the D/A conversion voltage V0 to V255 is carried out inthe microcomputer 1, a certain allowable value is provided with respectto each of the D/A conversion voltages, and a voltage value of thedesired waveform stored in the internal memory is read in order inaccordance with time series, a timing becomes able to be determined asthe timing at which each of the D/A conversion voltages V0 to V255 iswithin the allowable value.

The voltmeter 4 was described as a part connected to the D/A converter 2and the microcomputer 1. The voltmeter 4 may be provided so that thevoltmeter 4 is released from the D/A converter 2 and microcomputer 1after the D/A conversion voltage is measured during the generation ofthe desired D/A input data. The voltmeter 4 may be provided only when aD/A conversion voltage is measured, and may be removed from a productafter the measurement is conducted.

The voltmeter 4 may also be made of an A/D converter.

The desired waveform signal 6 was shown as a signal increasing to a 256stage of the D/A conversion voltage of V0 to V255 with time series. Thissignal may increase and decrease within the range in which the D/Aconverter 2 can convert the desired waveform signal 6. The number ofbits of the D/A converter 2 may also be other than 8 bits at which theD/A conversion voltage is converted into 256 stages. An arbitrary D/Aconversion voltage range may be set, for example, to a range havingsubstantially equal to widths around V128 expressed as V128+-ΔV, or V100to V200 etc.

The microcomputer 1 may be formed so as to generate desired D/A inputdata corresponding to a desired waveform, and gives the data to the D/Aconverter 2. All or some of these actions may be made as individualfunctional circuits.

Thus, according to this embodiment, it becomes possible to generate aD/A conversion voltage in which an error occurring due to numericirregularities of the D/A conversion element such as a resistorconstituting the D/A converter was corrected, by generating aD/A-converted voltage in accordance with the desired voltage on thebasis of the D/A conversion data obtained by varying input data into theD/A converter 2 by a minimum conversion unit or by a unit obtained bymultiplying the minimum conversion unit by an integer.

An example of the desired D/A input data outputted from themicrocomputer 1 will now be described more in detail.

The microcomputer 1 outputs an input value (which will hereinafter bereferred to as DAC input value), which designates D/A conversion voltageas desired D/A input data, into the D/A converter 2. The microcomputer 1may store the timing (at which the D/A-converted voltage in the D/Aconversion data and a voltage of a desired waveform varying with timeseries become substantially equal to each other) shown in FIG. 4 in theinternal memory of the microcomputer 1.

For example, the voltage VO shown in FIG. 2 is provided to the DAC inputvalue 00, while the voltage V255 is provided to the DAC input value FF.The microcomputer 1 stores (the timing t0 corresponding to the DAC inputvalue 00 is a timing 0) the timing t1 to t256 at which the DAC inputvalues 01 (corresponding to the voltage V1) to FF (corresponding to thevoltage V255) are inputted into the D/A converter 2 correspondingly toeach of the DAC input value. The microcomputer 1 outputs the DAC inputvalue to the D/A converter 2 in accordance with the stored data.

The D/A 2 outputs an analog signal providing a voltage corresponding tothe DAC input value. For example, a voltage corresponding to the voltageV0 is outputted with respect to the DAC input value 00, and a voltagecorresponding to the voltage V255 is outputted with respect to the DACinput value FF.

As the DAC input values, an initial value, the width of intervals ofincrement (or decrement) DAC input values and the number of increment(or decrement) are designated, and the DAC input value may be outputtedat the corresponding timing.

For example, when as initial values, DAC input value is k, the width ofintervals is 2 and frequency of occurrence of increment is n, a DACinput value k is outputted at a timing tk(=0), a DAC input value k+2 atthe timing tk+2, a DAC input value k+4 at a timing tk+4, . . . DAC inputvalue k+2n at a timing tk+2n and so forth.

In another embodiment the microcomputer 1 may store different values fordifferent temperatures correspondingly to desired D/A input data, and atiming for outputting a DAC input value may be computed at apredetermined temperature T.

For example, as the timing at which the DAC input value corresponds tothe voltage Vk, the timing tk(T1) at which the temperature is T1 and thetiming tk(T2) at which the temperature is T2 are obtained from theinternal memory of the microcomputer 1. When tk−1(T1)=tk−1(T2) is set atthe voltage of Vk−1, the timing tk(T) for outputting the output voltageVk at the temperature T is expressed by the equation (1).

tk(T)=(m2/m)·tk(T1)+(m1/m)·tk(T2)   (1)

wherein m=m1+m2; m1=T1−T and m2=T−T2.

The timing for outputting the DAC input value at the temperature of Tcorresponding to each voltage value may be determined in the same mannerin order.

The microcomputer 1 outputs to the D/A converter 2 the D/A input valuewhich is calculated on the basis of the timing of prescribed temperaturein order the DA input value corresponding to the desired D/A input data.

Embodiment 2

FIG. 5 shows a block diagram of the waveform generation method in theembodiment 2 for carrying out this invention. In the above-describedembodiment 1, the voltmeter 4 is connected to an output of the D/Aconverter 2. In this embodiment, the voltmeter 4 is connected to anoutput of LPF 3.

The operation of this embodiment is identical with that of theembodiment 1. It becomes possible to generate D/A conversion voltage inwhich the non-linearity and the like depending upon the voltageamplitude of the LPF 3 are corrected, in addition to the same effect ofthe embodiment 1 in which, owing to the voltmeter 4 connected to theoutput of the LPF 3, an error occurring due to numeric irregularities ofthe D/A conversion element, such as a resistor constituting the D/Aconverter 2 are corrected.

The voltmeter 4 was described as a part connected to the LPF 3 andmicrometer 1. The voltmeter 4 may also be so provided that, after theD/A conversion voltage is measured during the generation of the desiredD/A input data, the voltmeter 4 is released from the LPF 3 andmicrocomputer 1. The voltmeter 4 may be provided only when the D/Aconversion voltage is measured, and, after the measurement finishes, thevoltmeter may be removed from a product.

Embodiment 3

FIG. 6 shows a block diagram of the waveform generation method in theembodiment 3 for carrying out this invention. In the above-describedembodiment 1, the microcomputer 1 and D/A converter 2 are formed in onebody. In the embodiment 3, a microcomputer 7 and a voltmeter 8constitute an IC tester 9 so that the D/A conversion data of the D/Aconverter 2 are measured with the D/A converter 2 by itself.

The operation of this embodiment 3 is identical with that of theembodiment 1. The measured D/A conversion data are stored in advance inthe internal memory of the microcomputer 1 and used in which the D/Aconverter 2 is incorporated separately in one body. Thus, when the D/Aconversion data of the D/A converter 2 are measured with the D/Aconverter 2 itself in the IC tester 9, the data measurement can beconducted efficiently, so that a productivity can be improved.

Embodiment 4

FIG. 7 shows a block diagram of a FMCW radar device in the embodiment 4for carrying out this invention. In FIG. 7, desired D/A data areprovided to a D/A converter 2 in accordance with a desired waveformstored in a memory (not shown) contained in a microcomputer 10 in order,to generate D/A conversion voltage D/A-converted in accordance with thedesired waveform. This D/A conversion voltage is passed through alow-pass filter LPF 3, and a LPF output signal with a high-frequencycomponent, which occurs during the D/A conversion operation, removed isobtained. When this LPF output signal is provided to a voltage controloscillator (which will hereinafter be referred to as VCO) 11 as anoscillating means, a high-frequency signal varying an oscillatingfrequency in accordance with the desired waveform is generated. Thishigh-frequency signal is distributed by a directional coupler 12, andsent to a transmission antenna 13 and a mixer 14.

The transmission antenna 13 radiates the high-frequency signal as atransmission wave ahead of the radar device. When an object exists aheadof the radar device, the high-frequency signal is reflected on theobject, and the reflected wave which is time delayed is received as areception wave by a reception antenna 15, and sent to the mixer 14.

The mixer 14 generates a signal (which will hereinafter be referred toas a beat signal) representing a difference between the frequency of thereflected wave and that of the transmission wave distributed by thedirectional coupler 12. This beat signal is amplified in an amplifier16, thereafter digitized in a A/D converter 17, and processed in themicrocomputer to calculate a relative distance between the radar deviceand an object and a relative velocity thereof with respect to theobject.

When the desired D/A input data are generated, the microcomputer 10 usesthe D/A converter 2 and voltmeter 4 to be operated in the same manner asthat in the embodiment 1. The voltmeter 4 shown in FIG. 7 may beprovided only when the FMCW radar device is tested and regulated, andmay not be incorporated in the FMCW radar device.

FIG. 8 shows a frequency variation diagram for calculating the relativedistance between the radar device and an object, and the relativevelocity thereof with respect to the object. In FIG. 8, the lateral axisrepresents time, and the longitudinal axis represents the frequency.

The transmission wave is radiated from the transmission antenna 13 sothat its transmission frequency 18 is linearly increased in an UP Charpsection Tmu, and linearly decreased in a DOWN Charp section Tmd.

Where V represents the relative velocity of the radar device withrespect to the object, R the relative distance between the radar deviceand the object, C the velocity of light, λ transmission wavelength, Δf afrequency modulation width, and Tmu=Tmd=Tm, a Doppler frequency fd isexpressed by the equation (2). A distance frequency fr which isproportional to the distance and occurs due to a time difference betweena transmission frequency 18 and a reception frequency 19 is expressed bythe equation (3), a beat frequency fb1 in the UP Charp section Tmu bythe equation (4), and a beat frequency fb2 in the DOWN Charp section bythe equation (5).

fd=2·V/λ  (2)

fr=(2R·Δf)/(C·Tm)   (3)

fb1=|fd−fr|  (4)

fb2=|fd+fr|  (5)

When the distance frequency fr is larger than the Doppler frequency fd,the equation (6) is established.

2fr=fb1+fb2   (6)

When the equation (3) is substituted for the equation (6), the equation(7) which determines the relative distance R between the radar deviceand the object is lead out.

R(C·Tm)·(fb1+fb2)/(4·Δf)   (7)

The distance between the radar device and the object can be determinedby the beat frequency fb1 and beat frequency fb2 in the equation (7).When the distance frequency fr is calculated, the relative velocity canalso be determined by the equations (2), (4) and (5).

Here, the relation between a control voltage added to VCO of the FMCWradar device and an oscillation frequency is non-linear. Each VCO has anindividual difference, so that it is necessary to add a control voltageto VCO in accordance with the characteristics thereof. FIG. 9 is awaveform diagram of a desired waveform 20 set in advance so as tocorrect the non-linearity mentioned above. Transmission frequency 18 islinearly increased or linearly decreased as mentioned above. However,since the transmission frequency has a non-linearity, a control voltageadded to VCO does not become linear but becomes a high-order curve asshown by a desired waveform signal 20. The generation of desired D/Ainput data provided to the D/A converter 2 correspondingly to thedesired waveform signal 20 can be carried out in the same manner as thatfor the desired waveform signal 6 in the embodiment 1.

The voltmeter 4 was described as a part connected to the D/A converter 2and microcomputer 10. The voltmeter 4 may be provided so that thevoltmeter be released from the D/A converter 2 and microcomputer 10after the measurement of the D/A conversion voltage is measured duringthe generation of the desired D/A input data. The voltmeter 4 may beprovided only when the D/A conversion voltage is measured, and may beremoved from the FMCW radar device after the measurement finishes beingconducted.

The voltmeter 4 may be made of an A/D converter.

The desired waveform signal 20 may be increased and decreased within therange, in which the DA converter 2 can practice the conversionoperation, in the same manner as the desired waveform signal 6 in theembodiment 1. The number of bits of the D/A converter 2 may also beother than 8 bits at which the D/A conversion voltage is converted into256 stages. An arbitrary D/A conversion voltage range may be set, forexample, to a range having substantially equal to widths around V128expressed as V128+−ΔV, or V100 to V200 etc.

Thus, according to this embodiment, a D/A-converted voltage inaccordance with a desired voltage is generated on the basis of the D/Aconversion data obtained by varying the input data into the D/Aconverter 2, by a minimum conversion unit or a unit obtained bymultiplying the minimum conversion unit by an integer. It therebybecomes possible to generate a D/A conversion voltage in which an erroroccurring due to numeric irregularities of the D/A conversion element,such as a resistor etc. constituting the D/A converter 2 was corrected.

Since an error occurring due to numeric irregularities of the D/Aconversion element, such as a resistor, etc. constituting the D/Aconverter 2 can be corrected, the accuracy of the oscillating frequencyof VCO is improved, so that the measuring accuracy concerning a distancebetween the radar device and an object, or a relative velocity thereofwith respect to the object can be improved.

Since an error occurring due to numeric irregularities of the D/Aconversion element, such as a resistor, etc. constituting the D/Aconverter 2 can be corrected, it becomes possible to secure a necessaryaccuracy without employing a high bit number expensive D/A converter,and manufacture the radar device inexpensively.

It is a matter of course that the microcomputer 10, VCO 11, LPF 3 andD/A converter 2 be formed in a package separate from that for thetransmission antenna 13 and reception antenna 15.

INDUSTRIAL APPLICABILITY

Thus, this invention can improve the accuracy of the waveform generatedeven when the D/A conversion element, such as a resistor constitutingthe D/A converter has numeric irregularities thereof Therefore, theinvention is applied to a technical field of a waveform generationmethod and a radar device using a D/A converter.

1. Radar device comprising: a storage device for storing a timing atwhich a D/A-converted voltage in D/A conversion data obtained by varyinginput data into a D/A converter by a conversion unit level based on theD/A-converted voltage and a voltage of a desired waveform varying withtime series become substantially equal to each other; a waveform storagedevice for registering the input data at the timing; a controller forgiving the input data to the D/A converter at the timing; and a variableoscillator for varying an oscillation frequency in accordance with avariation of the D/A-converted voltage.
 2. Radar device according toclaim 1, wherein the desired waveform is set to a waveform which rendersconstant a rate of change of the oscillation frequency varying with timeseries.
 3. An oscillator for radar device comprising: a time storagedevice for storing a timing in correspondence with input data in aD/A-converter at which a D/A conversion voltage in D/A conversion dataobtained by varying the input data by a conversion unit level based onthe D/A-converted voltage of a desired waveform varying with time seriesbecome substantially equal to each other; a controller for providing theinput data to the D/A-converter at the timing; and a variable oscillatorfor varying an oscillation frequency in accordance with the variation ofthe D/A conversion voltage.
 4. A waveform generation method comprising:feeding input data to a D/A-converter, wherein measuring of the inputdata is achieved as unit levels, and converting each unit level, via theD/A-converter, into a related output conversion voltage; determining anorder of timing based on the output conversion voltage; associating theorder of timing with a predetermined desired D/A input data; andadjusting the order of timing in accordance with the output conversionvoltage to produce a desired waveform corresponding to the desired D/Ainput data.
 5. The waveform generation method of claim 4, wherein thedesired D/A input data is obtained by: connecting a voltage measuringdevice to a source of the output conversion voltage; measuring theoutput conversion voltage; and disconnecting the voltage measuringdevice from the source after obtaining measurement of the outputconversion voltage.